4.14) In a query, how do I detect if a field is NULL?
4.15) What is the difference between the various character types?
4.16.1) How do I create a serial/auto-incrementing field?
- 4.16.2) How do I get the value of a serial insert?
+ 4.16.2) How do I get the value of a SERIAL insert?
4.16.3) Don't currval() and nextval() lead to a race condition with
- other concurrent backend processes?
- 4.17) What is an oid? What is a tid?
+ other users?
+ 4.17) What is an OID? What is a TID?
4.18) What is the meaning of some of the terms used in PostgreSQL?
4.19) Why do I get the error "FATAL: palloc failure: memory
exhausted?"
5.1) I wrote a user-defined function. When I run it in psql, why does
it dump core?
- 5.2) What does the message: NOTICE:PortalHeapMemoryFree: 0x402251d0
- not in alloc set! mean?
+ 5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0
+ not in alloc set!" mean?
5.3) How can I contribute some nifty new types and functions to
PostgreSQL?
5.4) How do I write a C function to return a tuple?
- 5.5) I have changed a source file. Why does the recompile does not see
- the change?
+ 5.5) I have changed a source file. Why does the recompile not see the
+ change?
_________________________________________________________________
General Questions
The main mailing list is: pgsql-general@PostgreSQL.org. It is
available for discussion of matters pertaining to PostgreSQL. To
- subscribe, send a mail with the lines in the body (not the subject
- line)
+ subscribe, send mail with the following lines in the body (not the
+ subject line)
subscribe
end
1.9) How do I find out about known bugs or missing features?
- PostgreSQL supports an extended subset of SQL-92. See our TODO for a
- list of known bugs, missing features, and future plans.
+ PostgreSQL supports an extended subset of SQL-92. See our TODO list
+ for known bugs, missing features, and future plans.
1.10) How can I learn SQL?
1.12) How do I join the development team?
- First, download the latest sources and read the PostgreSQL Developers
+ First, download the latest source and read the PostgreSQL Developers
documentation on our web site, or in the distribution. Second,
subscribe to the pgsql-hackers and pgsql-patches mailing lists. Third,
submit high-quality patches to pgsql-patches.
There are about a dozen people who have commit privileges to the
PostgreSQL CVS archive. They each have submitted so many high-quality
- patches that it was a pain for the existing committers to keep up, and
- we had confidence that patches they committed were likely to be of
- high quality.
+ patches that it was impossible for the existing committers to keep up,
+ and we had confidence that patches they committed were of high
+ quality.
1.13) How do I submit a bug report?
some features they don't have, like user-defined types,
inheritance, rules, and multi-version concurrency control to
reduce lock contention. We don't have outer joins, but are
- working on them for our next release.
+ working on them.
Performance
PostgreSQL runs in two modes. Normal fsync mode flushes every
* Python(PyGreSQL)
* TCL(libpgtcl)
* C Easy API(libpgeasy)
- * Embedded HTML(PHP from http://www.php.net)
+ * Embedded HTML (PHP from http://www.php.net)
_________________________________________________________________
Administrative Questions
You either do not have shared memory configured properly in your
kernel or you need to enlarge the shared memory available in the
kernel. The exact amount you need depends on your architecture and how
- many buffers and backend processes you configure postmaster to run
- with. For most systems, with default numbers of buffers and processes,
- you need a minimum of ~1MB.
+ many buffers and backend processes you configure for the postmaster.
+ For most systems, with default numbers of buffers and processes, you
+ need a minimum of ~1MB.
3.5) When I try to start the postmaster, I get IpcSemaphoreCreate errors.
Why?
You should not create database users with user id 0 (root). They will
be unable to access the database. This is a security precaution
- because of the ability of any user to dynamically link object modules
+ because of the ability of users to dynamically link object modules
into the database engine.
3.9) All my servers crash under concurrent table access. Why?
reduces the transaction overhead. Also consider dropping and
recreating indices when making large data changes.
- There are several tuning things that can be done. You can disable
- fsync() by starting the postmaster with a -o -F option. This will
- prevent fsync()'s from flushing to disk after every transaction.
+ There are several tuning options. You can disable fsync() by starting
+ the postmaster with a -o -F option. This will prevent fsync()'s from
+ flushing to disk after every transaction.
You can also use the postmaster -B option to increase the number of
shared memory buffers used by the backend processes. If you make this
value is measured in kilobytes, and the default is 512 (ie, 512K).
You can also use the CLUSTER command to group data in tables to match
- an index. See the cluster(l) manual page for more details.
+ an index. See the CLUSTER manual page for more details.
3.11) What debugging features are available?
They are temporary files generated by the query executor. For example,
if a sort needs to be done to satisfy an ORDER BY, and the sort
- requires more space than the backend's -S parameter allows, then temp
- files are created to hold the extra data.
+ requires more space than the backend's -S parameter allows, then
+ temporary files are created to hold the extra data.
The temp files should be deleted automatically, but might not if a
backend crashes during a sort. If you have no backends running at the
BLCKSZ. To use attributes larger than 8K, you can also use the large
object interface.
- Row length limit will be removed in 7.1.
+ The row length limit will be removed in 7.1.
4.7)How much database disk space is required to store data from a typical
text file?
CREATE UNIQUE INDEX person_id_key ON person ( id );
See the create_sequence manual page for more information about
- sequences. You can also use each row's oid field as a unique value.
+ sequences. You can also use each row's OID field as a unique value.
However, if you need to dump and reload the database, you need to use
- pg_dump's -o option or COPY WITH OIDS option to preserve the oids.
+ pg_dump's -o option or COPY WITH OIDS option to preserve the OIDs.
Numbering Rows.
- 4.16.2) How do I get the back the generated SERIAL value after an insert?
+ 4.16.2) How do I get the value of a SERIAL insert?
One approach is to to retrieve the next SERIAL value from the sequence
object with the nextval() function before inserting and then insert it
INSERT INTO person (name) VALUES ('Blaise Pascal');
$newID = currval('person_id_seq');
- Finally, you could use the oid returned from the INSERT statement to
+ Finally, you could use the OID returned from the INSERT statement to
lookup the default value, though this is probably the least portable
approach. In perl, using DBI with Edmund Mergl's DBD::Pg module, the
oid value is made available via $sth->{pg_oid_status} after
$sth->execute().
4.16.3) Don't currval() and nextval() lead to a race condition with other
- concurrent backend processes?
+ users?
No. This is handled by the backends.
- 4.17) What is an oid? What is a tid?
+ 4.17) What is an OID? What is a TID?
OIDs are PostgreSQL's answer to unique row ids. Every row that is
- created in PostgreSQL gets a unique oid. All oids generated during
+ created in PostgreSQL gets a unique OID. All OIDs generated during
initdb are less than 16384 (from backend/access/transam.h). All
- user-created oids are equal or greater that this. By default, all
- these oids are unique not only within a table, or database, but unique
+ user-created OIDs are equal or greater that this. By default, all
+ these OIDs are unique not only within a table, or database, but unique
within the entire PostgreSQL installation.
- PostgreSQL uses oids in its internal system tables to link rows
- between tables. These oids can be used to identify specific user rows
- and used in joins. It is recommended you use column type oid to store
- oid values. You can create an index on the oid field for faster
+ PostgreSQL uses OIDs in its internal system tables to link rows
+ between tables. These OIDs can be used to identify specific user rows
+ and used in joins. It is recommended you use column type OID to store
+ OID values. You can create an index on the OID field for faster
access.
Oids are assigned to all new rows from a central area that is used by
- all databases. If you want to change the oid to something else, or if
- you want to make a copy of the table, with the original oid's, there
+ all databases. If you want to change the OID to something else, or if
+ you want to make a copy of the table, with the original OID's, there
is no reason you can't do it:
CREATE TABLE new_table(old_oid oid, mycol int);
SELECT old_oid, mycol INTO new FROM old;
DELETE FROM new;
COPY new WITH OIDS FROM '/tmp/pgtable';
- Tids are used to identify specific physical rows with block and offset
+ TIDs are used to identify specific physical rows with block and offset
values. Tids change after rows are modified or reloaded. They are used
by index entries to point to physical rows.
* retrieve, select
* replace, update
* append, insert
- * oid, serial value
+ * OID, serial value
* portal, cursor
* range variable, table name, table alias
Currently, we join subqueries to outer queries by sequential scanning
the result of the subquery for each row of the outer query. A
- workaround is to replace IN with EXISTS. For example, change:
+ workaround is to replace IN with EXISTS:
SELECT *
FROM tab
WHERE col1 IN (SELECT col2 FROM TAB2)
The problem could be a number of things. Try testing your user-defined
function in a stand alone test program first.
- 5.2) What does the message: NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
- alloc set! mean?
+ 5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
+ alloc set!" mean?
You are pfree'ing something that was not palloc'ed. Beware of mixing
malloc/free and palloc/pfree.
This requires wizardry so extreme that the authors have never tried
it, though in principle it can be done.
- 5.5) I have changed a source file. Why does the recompile does not see the
+ 5.5) I have changed a source file. Why does the recompile not see the
change?
The Makefiles do not have the proper dependencies for include files.
- You have to do a make clean and then another make. You have to do a
- make clean and then another make.
+ You have to do a make clean and then another make.
<A HREF="#3.1">3.1</A>) Why does <I>initdb</I> fail?<BR>
<A HREF="#3.2">3.2</A>) How do I install PostgreSQL somewhere other than
-/usr/local/pgsql?<BR>
-<A HREF="#3.3">3.3</A>) When I start the postmaster, I get a
+<I>/usr/local/pgsql?</I><BR>
+<A HREF="#3.3">3.3</A>) When I start the <i>postmaster</i>, I get a
<I>Bad System Call</I> or core dumped message. Why?<BR>
-<A HREF="#3.4">3.4</A>) When I try to start the postmaster, I get
+<A HREF="#3.4">3.4</A>) When I try to start the <i>postmaster</i>, I get
<I>IpcMemoryCreate</I> errors. Why?<BR>
-<A HREF="#3.5">3.5</A>) When I try to start the postmaster, I get
+<A HREF="#3.5">3.5</A>) When I try to start the <i>postmaster</i>, I get
<I>IpcSemaphoreCreate</I> errors. Why?<BR>
<A HREF="#3.6">3.6</A>) How do I prevent other hosts from accessing my
PostgreSQL database?<BR>
<A HREF="#4.15">4.15</A>) What is the difference between the
various character types?<BR>
<A HREF="#4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?<BR>
-<A HREF="#4.16.2">4.16.2</A>) How do I get the value of a serial insert?<BR>
-<A HREF="#4.16.3">4.16.3</A>) Don't currval() and nextval() lead to a
-race condition with other concurrent backend processes?<BR>
+<A HREF="#4.16.2">4.16.2</A>) How do I get the value of a
+<small>SERIAL</small> insert?<BR>
+<A HREF="#4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a
+race condition with other users?<BR>
-<A HREF="#4.17">4.17</A>) What is an oid? What is a tid?<BR>
+<A HREF="#4.17">4.17</A>) What is an <small>OID</small>? What is a
+<small>TID</small>?<BR>
<A HREF="#4.18">4.18</A>) What is the meaning of some of the terms
used in PostgreSQL?<BR>
-<A HREF="#4.19">4.19</A>) Why do I get the error "FATAL: palloc
-failure: memory exhausted?"<BR>
+<A HREF="#4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc
+failure: memory exhausted?"</I><BR>
<A HREF="#4.20">4.20</A>) How do I tell what PostgreSQL version I
am running? <BR>
<A HREF="#4.21">4.21</A>) My large-object operations get <I>invalid
large obj descriptor.</I> Why?<BR>
<A HREF="#4.22">4.22</A>) How do I create a column that will default to the
current time?<BR>
-<A HREF="#4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so
-slow?<BR>
+<A HREF="#4.23">4.23</A>) Why are my subqueries using
+<CODE><small>IN</small></CODE> so slow?<BR>
<A HREF="#4.24">4.24</A>) How do I do an <i>outer</i> join?<BR>
<H2><CENTER>Extending PostgreSQL</CENTER></H2>
<A HREF="#5.1">5.1</A>) I wrote a user-defined function. When I run
it in <I>psql,</I> why does it dump core?<BR>
-<A HREF="#5.2">5.2</A>) What does the message:
-<I>NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?<BR>
+<A HREF="#5.2">5.2</A>) What does the message
+<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?<BR>
<A HREF="#5.3">5.3</A>) How can I contribute some nifty new types and functions
to PostgreSQL?<BR>
<A HREF="#5.4">5.4</A>) How do I write a C function to return a
tuple?<BR>
<A HREF="#5.5">5.5</A>) I have changed a source file. Why does the
-recompile does not see the change?<BR>
+recompile not see the change?<BR>
<HR>
The main mailing list is: <A
HREF="mailto:pgsql-general@PostgreSQL.org">pgsql-general@PostgreSQL.org</A>.
It is available for discussion of matters pertaining to PostgreSQL.
-To subscribe, send a mail with the lines in the body (not
+To subscribe, send mail with the following lines in the body (not
the subject line)
<PRE>
<A HREF="http://www.PostgreSQL.org">http://www.PostgreSQL.org</A>
</BLOCKQUOTE><P>
-There is also an IRC channel on EFNet, channel #PostgreSQL.
+There is also an IRC channel on EFNet, channel <I>#PostgreSQL.</I>
I use the unix command <CODE>irc -c '#PostgreSQL' "$USER"
irc.phoenix.net.</CODE><P>
<H4><A NAME="1.8">1.8</A>) What documentation is available?</H4><P>
Several manuals, manual pages, and some small test examples are
-included in the distribution. See the /doc directory. You can also
+included in the distribution. See the <I>/doc</I> directory. You can also
browse the manual on-line at <A
HREF="http://www.PostgreSQL.org/docs/postgres">
http://www.PostgreSQL.org/docs/postgres</A>.
PostgreSQL supports an extended subset of SQL-92. See our
<A HREF="http://www.PostgreSQL.org/docs/todo.html">
-TODO</A>
for a list of known bugs, missing features, and future plans.<P>
+TODO</A>
list for known bugs, missing features, and future plans.<P>
<H4><A NAME="1.10">1.10</A>) How can I learn SQL?</H4><P>
<H4><A NAME="1.12">1.12</A>) How do I join the development team?</H4><P>
-First, download the latest sources and read the PostgreSQL Developers
+First, download the latest source and read the PostgreSQL Developers
documentation on our web site, or in the distribution.
-Second, subscribe to the pgsql-hackers and pgsql-patches mailing lists.
+Second, subscribe to the <I>pgsql-hackers</I> and <I>pgsql-patches</I> mailing lists.
Third, submit high-quality patches to pgsql-patches.<P>
There are about a dozen people who have commit privileges to
the PostgreSQL CVS archive. They each have submitted so many
-high-quality patches that it was a pain for the existing
+high-quality patches that it was impossible for the existing
committers to keep up, and we had confidence that patches they
-committed were likely to be of high quality.
+committed were of high quality.
<H4><A NAME="1.13">1.13</A>) How do I submit a bug report?</H4><P>
integrity, and sophisticated locking. We have some features they don't
have, like user-defined types, inheritance, rules, and multi-version
concurrency control to reduce lock contention. We don't have outer
-joins, but are working on them for our next release.<BR><BR>
+joins, but are working on them.<BR><BR>
<DT> <B>Performance</B>
<DD>
<LI>Python(PyGreSQL)
<LI>TCL(libpgtcl)
<LI>C Easy API(libpgeasy)
-<LI>Embedded HTML(<A HREF="http://www.php.net">PHP from http://www.php.net</A>)
+<LI>Embedded HTML
(<A HREF="http://www.php.net">PHP from http://www.php.net</A>)
</UL><P>
<HR>
<H4><A NAME="3.2">3.2</A>) How do I install PostgreSQL somewhere
-other than
/usr/local/pgsql?</H4><P>
+other than
<I>/usr/local/pgsql?</I></H4><P>
-The simplest way is to specify the --prefix option when running configure.
-If you forgot to do that, you can edit Makefile.global and change POSTGRESDIR
-accordingly, or create a
Makefile.custom and define POSTGRESDIR there.<P>
+The simplest way is to specify the --prefix option when running <I>configure.</I>
+If you forgot to do that, you can edit <I>Makefile.global</I> and change POSTGRESDIR
+accordingly, or create a
<I>Makefile.custom</I> and define POSTGRESDIR there.<P>
-<H4><A NAME="3.3">3.3</A>) When I start the postmaster, I get a <I>Bad
+<H4><A NAME="3.3">3.3</A>) When I start the <i>postmaster</i>, I get a <I>Bad
System Call</I> or core dumped message. Why?</H4><P>
It could be a variety of problems, but first check to see that you
kernel support for shared memory and semaphores.<P>
-<H4><A NAME="3.4">3.4</A>) When I try to start the postmaster, I
+<H4><A NAME="3.4">3.4</A>) When I try to start the <i>postmaster,</i> I
get <I>IpcMemoryCreate</I> errors. Why?</H4><P>
You either do not have shared memory configured properly in your kernel or
you need to enlarge the shared memory available in the kernel. The
exact amount you need depends on your architecture and how many buffers
-and backend processes you configure postmaster to run with.
+and backend processes you configure for the <i>postmaster.</i>
For most systems, with default numbers of buffers and processes, you
need a minimum of ~1MB.<P>
-<H4><A NAME="3.5">3.5</A>) When I try to start the postmaster, I
+<H4><A NAME="3.5">3.5</A>) When I try to start the <i>postmaster,</i> I
get <I>IpcSemaphoreCreate</I> errors. Why?</H4><P>
If the error message is <I>IpcSemaphoreCreate: semget failed (No space
left on device)</I> then your kernel is not configured with enough
semaphores. Postgres needs one semaphore per potential backend process.
-A temporary solution is to start the postmaster with a smaller limit on
+A temporary solution is to start the <i>postmaster</i> with a smaller limit on
the number of backend processes. Use <I>-N</I> with a parameter less
than the default of 32. A more permanent solution is to increase your
kernel's <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI</SMALL> parameters.<P>
The default configuration allows only unix domain socket connections
from the local machine. To enable TCP/IP connections, make sure the
-postmaster has been started with the <I>-i</I> option, and add an
+<i>postmaster</i> has been started with the <I>-i</I> option, and add an
appropriate host entry to the file
<I>pgsql/data/pg_hba.conf</I>.
user?</H4><P>
You should not create database users with user id 0 (root). They will be
-unable to access the database. This is a security precaution because
-of the ability of any user to dynamically link object modules into the
+unable to access the database. This is a security precaution because
+of the ability of users to dynamically link object modules into the
database engine.<P>
consider dropping and recreating indices when making large data
changes.<P>
-There are several tuning things that can be done. You can disable
-<I>fsync()</I> by starting the postmaster with a <I>-o -F</I> option. This will
-prevent <I>fsync()'s</I> from flushing to disk after every transaction.<P>
+There are several tuning options. You can disable
+<I>fsync()</I> by starting the <I>postmaster</I> with a <I>-o -F</I>
+option. This will prevent <I>fsync()'s</I> from flushing to disk after
+every transaction.<P>
-You can also use the postmaster -B option to increase the number of
+You can also use the <I>postmaster</I> <I>-B</I> option to increase the number of
shared memory buffers used by the backend processes. If you make this
-parameter too high, the postmaster may not start because you've exceeded
+parameter too high, the <I>postmaster</I> may not start because you've exceeded
your kernel's limit on shared memory space.
Each buffer is 8K and the default is 64 buffers.<P>
-You can also use the backend -S option to increase the maximum amount
-of memory used by the backend process for temporary sorts. The -S value
+You can also use the backend <I>-S</I> option to increase the maximum amount
+of memory used by the backend process for temporary sorts. The <I>-S</I> value
is measured in kilobytes, and the default is 512 (ie, 512K).<P>
You can also use the <SMALL>CLUSTER</SMALL> command to group data in tables to
-match an index. See the
cluster(l) manual page for more details.<P>
+match an index. See the
<small>CLUSTER</small> manual page for more details.<P>
<H4><A NAME="3.11">3.11</A>) What debugging features are available?</H4><P>
PostgreSQL has several features that report status information that can
be valuable for debugging purposes.<P>
-First, by running configure with the --enable-cassert option, many
+First, by running <I>configure</I> with the --enable-cassert option, many
<I>assert()'s</I> monitor the progress of the backend and halt the program when
something unexpected occurs.<P>
This will put a server.log file in the top-level PostgreSQL directory.
This file contains useful information about problems or errors
-encountered by the server. <I>Postmaster</I> has a -d option that allows even
+encountered by the server. <I>Postmaster</I> has a <I>-d</I> option that allows even
more detailed information to be reported. The <I>-d</I> option takes a number
that specifies the debug level. Be warned that high debug level values
generate large log files.<P>
<H4><A NAME="3.12">3.12</A>) I get 'Sorry, too many clients' when trying
to connect. Why?</H4><P>
-You need to increase the postmaster's limit on how many concurrent backend
+You need to increase the <i>postmaster's</i> limit on how many concurrent backend
processes it can start.<P>
In PostgreSQL 6.5 and up, the default limit is 32 processes. You can
-increase it by restarting the postmaster with a suitable <I>-N</I>
+increase it by restarting the <i>postmaster</i> with a suitable <I>-N</I>
value. With the default configuration you can set <I>-N</I> as large as
1024. If you need more, increase <SMALL>MAXBACKENDS</SMALL> in
<I>include/config.h</I> and rebuild. You can set the default value of
-<I>-N</I> at configuration time, if you like, using configure's
+<I>-N</I> at configuration time, if you like, using <I>configure's</I>
<I>--with-maxbackends</I> switch.<P>
Note that if you make <I>-N</I> larger than 32, you must also increase
-<I>-B</I> beyond its default of 64; -B must be at least twice -N, and
+<I>-B</I> beyond its default of 64; <I>-B</I> must be at least twice <I>-N,</I> and
probably should be more than that for best performance. For large
numbers of backend processes, you are also likely to find that you need
to increase various Unix kernel configuration parameters. Things to
They are temporary files generated by the query executor. For
example, if a sort needs to be done to satisfy an <SMALL>ORDER BY,</SMALL> and
the sort requires more space than the backend's <I>-S</I> parameter allows,
-then temp files are created to hold the extra data.<P>
+then temp
orary files are created to hold the extra data.<P>
The temp files should be deleted automatically, but might not if a backend
crashes during a sort. If you have no backends running at the time,
commas, decimal points, and date formats.</H4><P>
Check your locale configuration. PostgreSQL uses the locale setting of
-the user that ran the postmaster process. There are postgres and psql
+the user that ran the <i>postmaster</i> process. There are postgres and psql
SET commands to control the date format. Set those accordingly for
your operating environment.<P>
<SMALL>BLCKSZ.</SMALL> To use attributes larger than 8K, you can also
use the large object interface.<P>
-
Row length limit will be removed in 7.1.<P>
+
The row length limit will be removed in 7.1.<P>
<H4><A NAME="4.7">4.7</A>)How much database disk space is required to
</PRE>
See the <I>create_sequence</I> manual page for more information about sequences.
-You can also use each row's <I>oid</I> field as a unique value. However, if
+You can also use each row's <I>OID</I> field as a unique value. However, if
you need to dump and reload the database, you need to use <I>pg_dump's -o</I>
-option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the
oids.<P>
+option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the
<small>OID</small>s.<P>
<A HREF="http://www.PostgreSQL.org/docs/aw_pgsql_book">Numbering Rows.</A>
-<H4><A NAME="4.16.2">4.16.2</A>) How do I get the back the generated SERIAL value after an insert?</H4><P>
+<H4><A NAME="4.16.2">4.16.2</A>) How do I get the value of a
+<small>SERIAL</small> insert?</H4><P>
One approach is to to retrieve the next SERIAL value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the example table in <A HREF="#4.16.1">4.16.1</A>, that might look like this:
<PRE>
$newSerialID = nextval('person_id_seq');
INSERT INTO person (name) VALUES ('Blaise Pascal');
$newID = currval('person_id_seq');
</PRE>
-Finally, you could use the <A HREF="#4.17">oid</A> returned from the
+Finally, you could use the <A HREF="#4.17"><small>OID</small></A> returned from the
INSERT statement to lookup the default value, though this is probably
the least portable approach. In perl, using DBI with Edmund Mergl's
DBD::Pg module, the oid value is made available via
<I>$sth->{pg_oid_status} after $sth->execute().</I>
-<H4><A NAME="4.16.3">4.16.3</A>) Don't currval() and nextval() lead to a race condition with other
-
concurrent backend processes?</H4><P>
+<H4><A NAME="4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to
+
a race condition with other users?</H4><P>
No. This is handled by the backends.
-<H4><A NAME="4.17">4.17</A>) What is an oid? What is a tid?</H4><P>
+<H4><A NAME="4.17">4.17</A>) What is an <small>OID</small>? What is a
+<small>TID</small>?</H4><P>
<small>OID</small>s are PostgreSQL's answer to unique row ids. Every row that is
-created in PostgreSQL gets a unique <small>oid</small>. All <small>oid</small>s generated during
+created in PostgreSQL gets a unique <small>OID</small>. All <small>OID</small>s generated during
<I>initdb</I> are less than 16384 (from <I>backend/access/transam.h</I>). All
-user-created <small>oid</small>s are equal or greater that this. By default, all these
-<small>oid</small>s are unique not only within a table, or database, but unique within
+user-created <small>OID</small>s are equal or greater that this. By default, all these
+<small>OID</small>s are unique not only within a table, or database, but unique within
the entire PostgreSQL installation.<P>
-PostgreSQL uses <small>oid</small>s in its internal system tables to link rows between
-tables. These <small>oid</small>s can be used to identify specific user rows and used
-in joins. It is recommended you use column type <small>oid</small> to store <small>oid</small>
-values. You can create an index on the <small>oid</small> field for faster access.<P>
+PostgreSQL uses <small>OID</small>s in its internal system tables to link rows between
+tables. These <small>OID</small>s can be used to identify specific user rows and used
+in joins. It is recommended you use column type <small>OID</small> to
+store <small>OID</small>
+values. You can create an index on the <small>OID</small> field for faster access.<P>
-<small>Oid</small>s are assigned to all new rows from a central area that is used by
-all databases. If you want to change the <small>oid</small> to something else, or if
-you want to make a copy of the table, with the original <small>oid</small>'s, there is
+O<small>id</small>s are assigned to all new rows from a central area that is used by
+all databases. If you want to change the <small>OID</small> to something else, or if
+you want to make a copy of the table, with the original <small>OID</small>'s, there is
no reason you can't do it:
<PRE>
-->
</PRE><P>
-Tids are used to identify specific physical rows with block and offset
+T<small>ID</small>s are used to identify specific physical rows with block and offset
values. Tids change after rows are modified or reloaded. They are used
by index entries to point to physical rows.<P>
<LI> retrieve, select
<LI> replace, update
<LI> append, insert
-<LI> oid, serial value
+<LI> <small>OID</small>, serial value
<LI> portal, cursor
<LI> range variable, table name, table alias
</UL><P>
-<H4><A NAME="4.19">4.19</A>) Why do I get the error "FATAL: palloc
-failure: memory exhausted?"<BR></H4><P>
+<H4><A NAME="4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc
+failure: memory exhausted?"<
/I><BR></H4><P>
It is possible you have run out of virtual memory on your system, or
your kernel has a low limit for certain resources. Try this before
-starting the postmaster:
+starting the <i>postmaster:</i>
<PRE>
ulimit -d 65536
CREATE TABLE test (x int, modtime timestamp default now() );
</PRE></CODE>
<P>
-<H4><A NAME="4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so
-slow?<BR></H4><P>
+<H4><A NAME="4.23">4.23</A>) Why are my subqueries using
+
<CODE><small>IN</small></CODE> so slow?<BR></H4><P>
Currently, we join subqueries to outer queries by sequential scanning
the result of the subquery for each row of the outer query. A workaround
-is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>. For example,
-change:
+is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>:
<CODE><PRE>
SELECT *
FROM tab
The problem could be a number of things. Try testing your user-defined
function in a stand alone test program first.
-<H4><A NAME="5.2">5.2</A>) What does the message:
-<I>
NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?</H4><P>
+<H4><A NAME="5.2">5.2</A>) What does the message
+<I>
"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?</H4><P>
You are <I>pfree'ing</I> something that was not <I>palloc'ed.</I>
Beware of mixing <I>malloc/free</I> and <I>palloc/pfree.</I>
tried it, though in principle it can be done.<P>
<H4><A NAME="5.5">5.5</A>) I have changed a source file. Why does the
-recompile
does not see the change?</H4><P>
+recompile not see the change?</H4><P>
-The Makefiles do not have the proper dependencies for include files. You
-have to do a <I>make clean</I> and then another <I>make</I>.
- You
-have to do a <I>make clean</I> and then another <I>make.</I><P>
+The <I>Makefiles</I> do not have the proper dependencies for include files. You
+have to do a <I>make clean</I> and then another <I>make</I>.<P>
</BODY>
OSDN Git Service
